Guide tones are usually the third and seventh scale degree of a seventh chord, and are also the most active voices in most chord progressions, as these are the voices that move by half-step or whole-step from chord to chord. The guide tones are the most important notes in the chords that make the harmony function or move. When playing chord progressions on piano, it is important to connect the guide tones from chord to chord in order to fully outline the functioning harmony for the audience or other musicians.
The exercise below isolates only the guide tones from each chord to the right hand, while the left hand plays a simple single-note bass line.